1. Field of the Invention
The invention is related to a color filter array, and particularly, to a color filter array having enlarged color filters or extended edges at corners thereof that is capable of preventing color filter from peeling.
2. Description of the Prior Art
Image sensor includes CMOS image sensors (CIS) and charged-coupled devices (CCD). CMOS image sensors use the materials and technology of semiconductor processes to create photosensitive devices that capture and process an optical image within a single integrated chip. CMOS image sensors are utilized in many industrial and consumer sectors, such as cell phones, personal digital assistants, and industrial digital cameras, etc.
A CMOS image sensor includes a substrate, a plurality of photodiodes, metal interconnects, color filter array and a plurality of microlenses to construct pixels for sensing images. Lights strike the CMOS image sensor through the topmost microlens and are separated by color filters according to their wavelength. The separated lights strike the photodiodes and induce electronic signals. These signals are recorded and processed by other components of the CMOS image sensor. Pixels of the CMOS image sensor are arranged in a pixel array. The pixel array includes an active sensor region composed of an active pixel array, and a dummy pixel array surrounding the active sensor region. The dummy pixel array protects the active pixel array in the active sensor region. In addition, signals generated by the dummy pixel array are used as references of the signals generated by the active pixel array to calibrate noises resulted from CMOS image sensor.
Please refer to FIG. 1. FIG. 1 is a schematic diagram illustrating a color filter array 10 of a conventional CMOS image sensor. The color filter array 10 includes an active pixel area in an active sensor region and a dummy pixel array surrounding the active sensor area. The color filter array 10 has a plurality of red color filters (R) 12, a plurality of green color filters (G) 14, and a plurality of blue color filters (B) 16. Four color filters (G, R, G, B) is a pixel unit, and therefore, the mosaic color filter array is formed by a plurality of pixel units. These color filters separate lights according to their wavelength so that the CMOS image sensor may sense colorful images.
The color filter array uses color photoresist as material, and is formed by several processes in sequence to form the color filters, such as coating, exposing, developing, and baking. Each kind of color filters is formed on the substrate individually, and then, these color filters are pieced up to form the color filter array. Referring to FIG. 2, a cross-sectional view of a red color filter, a green color filter, and a blue color filter made of negative photoresist is shown. Since each kind of negative color photoresist has individual photosensitivity, each kind of color filter has varied cross-sectional shapes. The fabricating processes are performed to form posterior color filters. For instance, developing and cleaning often results in peeling of prior formed color filters from the substrate, especially for the blue color filters, which have the smallest bottom area. Please refer to FIG. 3. FIG. 3 is a schematic diagram illustrating a part of the dummy pixel array, which surrounds the active sensor region. The peeling of color filter is found at the edge or corner of the color filter array. Based on our data, 80% of the color filters that get peeled are peeled from corners of the color filter array. The peeling of color filters is a major problem of fabricating and substantially reduces yield of the product.